1. Field of the Invention
Embodiments of the present invention relate to a piezoelectric actuator, a method of manufacturing the piezoelectric actuator, a liquid discharge head, a method of manufacturing the liquid discharge head, and an image forming device.
2. Description of the Related Art
As an image forming device such as a printer, a facsimile machine, a copier, a plotter, or a combined machine thereof, an image forming device (an ink jet recording device) of a liquid discharge recording type that utilizes a recording head including a liquid discharge head (a liquid droplet discharge head) that discharges an ink droplet is known. The image forming device of the liquid discharge recording type forms an image (recording, typing, imaging, and printing are used as synonyms) by discharging ink droplets from the recording head onto a sheet being conveyed. Here, the sheet is not limited to a paper, but includes an OHP and the like. The sheet means something to which an ink droplet or another liquid can be adhered. It may be referred to as a medium to be recorded on, a recording medium, a recording paper, or a recording sheet. There are two types of the image forming devices of the liquid discharge recording type. Namely, one of them is an image forming device of serial type, in which a recording head forms an image when the recording head moves in the main scanning direction while discharging liquid droplets. The other one is an image forming device of line type which utilizes a line-type head.
In the present specification, the image forming device of liquid discharge recording type is a device which forms an image by discharging a liquid onto a medium, such as a paper, a line, a fiber, a fabric, a leather, a metal, a plastic, a glass, a timber, or a seramic. Further, “forming an image” means not only to add an image having a meaning, such as a character or a graphic, to a medium, but also to add an image having no meaning, such as a pattern, to a medium (simply to apply liquid droplets to the medium). Further, “an ink” means not only a usual ink, but is also a generic term of a liquid with which an image can be formed, such as a recording liquid, a fixing liquid, or a fluid. For example, a DNA sample, a resist, a pattern material, and a resin are included in “inks.” Further, “an image” means not only a two-dimensional image, but also an image attached to something which is formed three-dimensionally and an image which is formed three-dimensionally.
As a liquid discharge head, a so-called piezoelectric type head is known. Here, the piezoelectric type head includes a piezoelectric body as a pressure generating means that applies pressure to an ink, that is, for example, a liquid inside a liquid chamber, and, especially, a piezoelectric actuator in which plural piezoelectric elements (piezoelectric poles) are formed by grooving a laminated piezoelectric member in which piezoelectric layers and internal electrodes are alternately laminated. The piezoelectric type head causes an oscillation plate, which can be elastically deformed and which forms a wall surface in the liquid chamber, to be deformed by a displacement of a laminated piezoelectric element in d33 direction or in d31 direction; causes volume and pressure inside the liquid chamber to vary; and discharges liquid droplets (cf. Patent Document 1 (Japanese Published Unexamined Application No. 2010-201785)).
In such a piezoelectric type head, the piezoelectric poles and a driving circuit are connected by a flexible wiring substrate, such as a FPC, on which wiring electrodes corresponding to the piezoelectric poles are formed, so as to apply driving currents to the piezoelectric poles. Therefore, when the density is to be increased by reducing an arrangement pitch of the piezoelectric poles, reliability of the connection between the piezoelectric poles and the flexible wiring substrate may need to be ensured.
In order to ensure the reliability of the connection between the piezoelectric poles and the flexible wiring substrate, connecting areas may required to be broadened. However, in accordance with the increase of the density, the piezoelectric poles become thinner. Thus it is difficult to broaden the connecting areas. Further, since a distance between the neighboring piezoelectric poles is narrower, shorts between the neighboring piezoelectric poles and between the neighboring wiring electrodes become problems. Especially, since an accumulated pitch error in the arrangement direction of the wiring electrodes of the flexible wiring substrate formed with a resin material varies depending on processing accuracy or a storage environment, a positional shift error on the position, at which the piezoelectric pole and the wiring electrode are connected, occurs, and a short is more likely to be occurred.
Conventionally, it is known that, in order to prevent a short between the neighboring piezoelectric poles from occurring, solder joint portions between the piezoelectric poles and the wiring electrodes are arranged in a staggered fashion. With this arrangement, even if the solder flows out, pieces of the solder flowing out from the neighboring electrodes do not make contact (cf. Patent Document 2 (Japanese Published Unexamined Application No. H07-156376)).
Further, a configuration is known such that an effective width of a conductive pattern at a connecting portion of a flexible tape is set to be greater than a width of a piezoelectric oscillator, and a non-overlapping area that does not overlap with the conductive pattern is provided at a connecting portion of the piezoelectric oscillator. With such a configuration, an excessive amount of the solder melted at the time of connecting the conductive pattern is released to the non-overlapping area (cf. Patent Document 3 (Japanese Published Unexamined Application No. 2000-117973)).
In an image forming device, in order to form a higher quality image, the size of liquid droplets is reduced and nozzles are more densely formed. Further, in order to handle a higher processing speed, a higher frequency is used for a driving frequency, and a head, such as the line-type head, is lengthened in accordance with an increase of the number of the nozzles per head.
In order to accept higher integration, such as the increased density of the nozzles, the piezoelectric poles, as piezoelectric actuators which greatly affect a droplet discharging characteristic, may be required to be highly integrated. Further, when a laminated piezoelectric element is used, in order to ensure a desired displacement amount, a separation groove may be required to be deepened, namely, heights of the piezoelectric poles may be required to be increased. Thus, there is a problem that the piezoelectric poles that are evenly spaced apart at a fine pitch and that have a high aspect ratio may be required to be formed.
Further, when the piezoelectric poles are formed by grooving the laminated piezoelectric element, if the piezoelectric poles are densely produced, stiffness of the piezoelectric poles is decreased. Thus the piezoelectric poles are deformed by a processing load and the piezoelectric poles tend to be inclined. Therefore, the inclined piezoelectric poles and the wiring electrodes, which are arranged in parallel, may be required to be connected.
It has been found that, when the piezoelectric poles are inclined, a short between the neighboring piezoelectric poles may occur, even if the configuration disclosed in Patent Document 2 is applied. Further, for the configuration disclosed in Patent Document 3, there is a problem that, since a substantial pattern width (a width of the wiring electrodes) is increased, the configuration may not be applied for connecting the densely arranged piezoelectric poles and the wiring electrodes.
Embodiments of the present invention have been developed in view of the above described problems. An objective of the embodiments is to achieve a higher integration of piezoelectric poles, which are evenly spaced apart at a fine pitch, and which have a high aspect ratio.
Further, it is an objective of the embodiments to prevent a failure, such as a short, from occurring, even if the piezoelectric poles are inclined or there is an error in the pitch of wiring electrodes of a flexible wiring substrate.